Inorganic materials may be used in composite articles to strengthen and reinforce the articles. In addition to increased dimensional stability, addition of the inorganic material provides polymer composites with significantly improved physical and mechanical properties. As one example, glass fibers may be placed into a polymer matrix where the high tensile strength of glass causes the matrix to become more rigid. The glass fibers incorporated in the polymer matrix may take various forms, such as continuous or chopped strands, rovings, woven or non-woven fabrics, and continuous or chopped strand mats.
Conventionally, glass fibers are formed by attenuating streams of a molten glass material from a bushing or orifice. The glass fibers may be attenuated by pulling by a winder, which collects filaments into a package or by other equipment or method capable of pulling the fibers. A sizing composition, or chemical treatment, is typically applied to the fibers after they are drawn from the bushing. After the fibers are treated with the sizing, which is typically in aqueous form, they may be dried in a package, chopped, or kept in the wet state before downstream processing.
Fiberglass may be mixed with a polymeric resin in an extruder and supplied to a compression- or injection-moulding machine to be formed into glass fiber-reinforced plastic composites. Typically, polymer pellets and fiberglass are fed together or separately into an extruder. During the extrusion process using single or twin-screw machines, the resin is melted and the fibers are dispersed throughout the molten resin to form a fiber/resin mixture. Next, the fiber/resin mixture may be degassed, cooled, and formed into pellets. The dry fiber strand/resin dispersion pellets are then fed to a moulding machine and formed into moulded composite articles that have a substantially homogeneous dispersion of glass fiber strands throughout the composite article.
Alternatively, in the process using continuous filaments, fiberglass filaments are mixed with the molten resin in an extruder with the screw geometry designed to mix the matrix with fibers without causing significant damage to the fibers. Obtained extruded materials are then subjected to compression moulding to form long-fiber reinforced thermoplastic materials with significantly improved mechanical properties due to the mostly unidirectional distribution of fiber.
Various chemical treatments exist for inorganic surfaces such as glass fibers to aid in their processability and applications. After fiber formation and before bundling, the filaments or fibers may be treated with a coating composition (sometimes referred to as a “sizing composition”) that is applied to at least a portion of the surface of the individual filaments to protect them from abrasion, improve the chemical or physical bonding, and to assist in processing.
As used herein, the term “sizing composition”, refers to any such coating composition applied to the filaments after forming. Sizing compositions may provide protection for subsequent processing steps, such as those where the fibers pass by contact points as in the winding of the fibers and strands onto a forming package, drying the sized fibers to remove the water and/or other solvent or melting of the film former on the fiber surface, twisting from one package to a bobbin, beaming to place the yarn onto very large packages ordinarily used as the warp in a fabric, chopping in a wet or dry condition, roving into larger bundles or groups of strands, unwinding, and other downstream processes. In addition, sizing compositions can play a dual role when placed on fibers that reinforce polymeric matrices in the production of fiber-reinforced plastics. In such applications, the sizing composition can provide protection as well as compatibility and/or chemical bonding between the fiber and the matrix polymer. Conventional sizing compositions typically contain one or more film forming polymeric or resinous components, glass-resin coupling agents, and one or more lubricants dissolved or dispersed in a liquid medium. The film forming component of the sizing composition is desirably selected to be compatible with the matrix resin or resins in which the glass fibers are to be embedded.
Many types of polymers may be reinforced by inorganic materials. Of particular note are those polymers formed by ring-opening polymerization reactions. Polyamides, such as poly(caprolactam), commonly know as “Nylon-6” or “polyamide-6”, are examples of resins formed by ring-opening polymerization that are frequently reinforced by glass fibers. There is a need to provide glass-reinforced polyamide composites with high glass loading; however, one of the barriers is the high polymer viscosity of the polyamide in the molten state. This high viscosity hinders the dispersion of the glass fibers throughout the molten resin when the fiber/resin mixture is formed.
Anionic-catalysed ring-opening polymerization of lactams has become a commercially significant method for preparation of PA resins since these polymerizations can be conducted at relatively low temperatures and under atmospheric pressures. Caprolactam is by far the most studied lactam for such reactions and Nylon-6 prepared by this route compares favorably in properties with that prepared by conventional hydrolytic polymerization. Fast reaction kinetics, absence of by-products, and the crystalline nature of the Nylon so produced also makes anionic polymerization of lactams a compelling choice for several industrial applications, including reactive extrusion, reactive thermoplastic pultrusion, and reaction injection molding.
There is a need for new compounds and methods that allow increased loading and dispersion of a reinforcing material in a polymer composite. For example, there is a need for compounds and methods to increase the loading and dispersion of fiberglass in polymer matrices of thermoplastic and thermoset polymers These and other needs are addressed in the present application.